This invention relates to Dense Wavelength Multiplex Systems (DWDMs) and specifically to securing information or channels in these systems.
Dense Wavelength Division Multiplex (DWDM) technology has provided a cost-effective solution to fiber exhaust in communications networks by increasing the data throughput of the network without requiring the installation of new fiber and is the enabling technology for the emerging all optical networking. In a DWDM system each of several input signals enter a DWDM node or network element and is assigned or converted to a specific wavelength, typically, in the 1550 nanometer (nm) band. After wavelength conversion each individual signal wavelength or channel is then multiplexed by wavelength division multiplexing and transmitted onto the same fiber. Consequently, a single fiber carries more than one wavelength. In fact each wavelength carried by a DWDM system may be considered a virtual fiber.
In order for DWDM technology to be truly viable as a network solution, DWDM systems must be secure. As opposed to re al fibers, the signal carried on the virtual fibers of DWDM systems may be susceptible to eavesdropping. In DWDM systems different channels travel through the same fiber and the same components. As a result of cross-talk, nonlinearity, etc., at the receiving end, there is a residual of signal(s) from other channels that can be isolated, amplified, and detected.
The potential for eavesdropping may be better appreciated by reference to FIG.1 where there is depicted a receiving node 100 in a DWDM network. Receiving node 100 may be an optical demultiplexer or add drop multiplexer, a wavelength converter, or an optical cross-connect that serves as a drop off or interchange point for one or more channels. FIG. 2 shows, on a logarithmic scale, the optical spectrum of channel 10 in FIG. 1 as it dropped from node 100. As FIG. 2 shows, although the goal was to drop only channel 10, channel 11 is clearly visible. In FIG. 3, I used a notch filter to reduce the optical signal to noise ratio (OSNR) for channel 10. As FIG. 3 shows, channel 11 is still present with enough power to be recoverable. In fact, in FIG. 4, I have turned off the channel 10 transmitter and as FIG. 4 shows there is a significant amount of residual power still present from channel 11. I have also achieved similar results shown in FIG. 4 by introducing a second filter to attenuate channel 10 in the received spectrum. In either case, in FIG. 4, channel 11 is leaked with large enough OSNR to be recoverable after optical amplification. I have achieved better than 20 dB OSNR for the leaked signal for this particular optically amplified DWDM system. I expect better eavesdropping performance (larger OSNR than 20 dB for the leaked signal) for DWDM systems without the amplified stimulated emission (ASE) associated with the optical amplification process. Accordingly, the user of channel of 10 may be able to recover channel 11 without the network operator ever knowing of the breach in security. On another level, residual power from each channel may be available on all the channels thereby providing for security akin to having a party line.
Of utility then would be a method and system for securing DWDM networks against potential eavesdropping.
My invention is a method and system for securing DWDM networks by introducing noise into the fiber channel or cable up to the level of cross-talk (leakage) or ASE noise, which ever is larger, so that unauthorized recovery of channels is prevented or not permitted.
In accordance with my invention, a white noise source inputs white noise into the fiber channel up to amplified spontaneous emission level so that only the signal intended to be dropped or terminated can be recovered. In accordance with my invention the added noise masks the leaked signal without affecting the performance of the channel intended to be dropped or terminated.
By using only a noise source the network is secured against eavesdropping without the need of any sophisticated monitoring or processing software. Accordingly, a DWDM system designed in accordance with my invention will not incur a substantial increase in cost.
In one aspect of my invention the noise source is included as part of the DWDM node at the point the multiwavelength signal is being received, i.e., at the point within the equipment before the multiwavelength signal is optically demultiplexed. Although the noise can be injected anywhere along the path of the multiwavelength signals, it is most effective if injected at the receiving end.
In another aspect of my invention the noise source is coupled onto the fiber after the optical demultiplexer and just before the single channel optical signal is being handed over. In this case only the channels that have to be secure get the noise injection. In accordance with this aspect of my invention, DWDM systems that have been already deployed may be protected by my invention.